23218

بررسي آزمايشگاهي تاثير استفاده از سرباره كوره آهن گدازي به منظور بهسازي خاك هاي رسي

كارشناسي ارشد

ژئوتكنيك

1399/6/30

دكتر نادر شريعتمداري

عمران

بسياري از خواص نامطلوب مرتبط با خاكهاي نرم همچون ظرفيت باربري پايين و قابليت تراكمپذيري بالا، نياز به تثبيت را در اين خاكها الزام ميبخشند. تثبيت شيميايي با آهك و سيمان يكي از متدوالترين روشها براي بهسازي اين خاكهاست؛ اگرچه توليد سيمان اثرات مخرب زيست محيطي چون آزادسازي مقادير زياد كربن دي اكسيد، مصرف قابل توجه انرژي و تسريع در اتمام منابع طبيعي را دارد. تمامي معايب مذكور ما را بر آن داشت كه امكانپذيري استفاده از مصالح سازگار با محيط زيست را به عنوان جايگزيني براي چسبانندههاي سنتي مورد بررسي قرار دهيم. در اين مطالعه امكانپذيري استفاده از ژئوپليمر بر پايه خاكستر آتشفشاني و سرباره كوره آهنگدازي به منظور بهسازي خاكهاي رسي مورد بررسي قرار گرفته است كه در آن به بررسي تاثير درصدهاي مختلف جايگزيني خاكستر آتشفشاني با سرباره، نسبت هاي مختلف فعالكننده به چسبانند، شرايط (دما) عملآوري و زمان عملآوري بر مقاومت نمونه ها پرداخته شده است. تست مقاومت فشاري تك محوري، تستهاي دوام ذوب-انجماد و تر-خشك، آناليزهاي XRD، FESEM-EDS-Mapping وFTIR به ترتيب به منظور مطالعه مشخصات مكانيكي، دوام و ريزساختار نمونهها انجام شده است نتايج اين پژوهش نشان داد كه اضافه كردن سرباره به خاكستر آتشفشاني منجر به عدم نياز به عمل آوري حرارتي نمونه ها شد و استفاده از آنها را در گسترههاي وسيعتري از دما و حتي دماي اتاق امكانپذير ساخت. به علاوه از آنجايي كه خاكستر آتشفشاني غني است از سيليكا و آلومينا و مقدار كمي اكسيد كلسيم دارد حال آنكه سرباره سرشار از اكسيد كلسيم است، حضور همزمان اين دو ماده در ژئوپليمر منجر به مقادير مقاومتي بالاتري شد كه اين موضوع به علت همافزايي تشكيل همزمان ژلهاي N-A-S-H و C-A-S-H بود. به علاوه نتايج تستهاي دوام نشان داد كه خاك تثبيت شده با ژئوپليمر عملكرد بهتري در برابر سيكلهاي ذوب-انجماد در مقايسه با سيكل هاي تر-خشك دارند. هم چنين نمونه هاي حاوي سرباره نسبت به نمونه هاي بدون سرباره كاهش مقاومت كمتري را در اثر قرار گرفتن در معرض سيكلهاي دوام تجربه كردند، كه اين موضوع اثر مثبت استفاده از سرباره را براي بهبود عملكرد در برابر سيكلهاي دوام نشان ميدهد. به علاوه كليه آناليزهاي ريزساختار اين مطالعه نتايج مقاومتي را به خوبي تاييد كردند.

1399/12/06

experimental study of the effect of using Ground Granulated blast furnance slag(GGBS) for improvement of clayley soil

9/20/2020 12:00:00 AM

Lots of undesirable properties associated with soft soils, including low bearing capacity and high compressibility, make it necessary for project sites to use a proper stabilization technique to meet engineering requirements. Chemical stabilization with lime and cement is a common method used for soft soil improvement. However, cement production is responsible for lots of destructive environmental impacts, such as high CO_2 emission, considerable energy consuming and accelerating the depletion of natural resources. All of the drawbacks above made us to investigate the possibility of using environmentally friendly materials as an alternative for traditional binders. An attempt in this study has been made to examine the feasibility of using VA-GGBS based geopolymers as a sustainable binder to stabilize clayey soil. The influence of different percentages of VA replaced by GGBS, activator/binder ratio, curing temperature, and curing time on compressive strength are investigated. The Unconfined Compressive Strength (UCS), freeze-thaw and wet-dry durability tests, X-ray diffraction (XRD), FESEM-EDS-Mapping and FTIR analysis have been utilized to study the mechanical, durability and microstructural properties of the geopolymer stabilized soil respectively. The results demonstrated that as volcanic ash requires elevated heat to be activated while, GGBS has a good reactivity at ambient temperature, utilizing a mixture of these two materials enables them to be applicable in wider ranges of temperatures which resulted in gaining desirable strengths in both curing conditions of OC and DC, however for all of the samples the curing condition of DC brought about higher strengths which was due to the better dissolution of aluminosilicates. Moreover, since volcanic ash is relatively high in silica and alumina but deficient in calcium oxide, while GGBS is rich in calcium oxide, the coexistence of these two materials in geopolymer was more efficient, which was due to the synergic formation of N-A-S-H and C-A-S-H gels. Investigating Lots of undesirable properties associated with soft soils, including low bearing capacity and high compressibility, make it necessary for project sites to use a proper stabilization technique to meet engineering requirements. Chemical stabilization with lime and cement is a common method used for soft soil improvement. However, cement production is responsible for lots of destructive environmental impacts, such as high CO_2 emission, considerable energy consuming and accelerating the depletion of natural resources. All of the drawbacks above made us to investigate the possibility of using environmentally friendly materials as an alternative for traditional binders. An attempt in this study has been made to examine the feasibility of using VA-GGBS based geopolymers as a sustainable binder to stabilize clayey soil. The influence of different percentages of VA replaced by GGBS, activator/binder ratio, curing temperature, and curing time on compressive strength are investigated. The Unconfined Compressive Strength (UCS), freeze-thaw and wet-dry durability tests, X-ray diffraction (XRD), FESEM-EDS-Mapping and FTIR analysis have been utilized to study the mechanical, durability and microstructural properties of the geopolymer stabilized soil respectively. The results demonstrated that as volcanic ash requires elevated heat to be activated while, GGBS has a good reactivity at ambient temperature, utilizing a mixture of these two materials enables them to be applicable in wider ranges of temperatures which resulted in gaining desirable strengths in both curing conditions of OC and DC, however for all of the samples the curing condition of DC brought about higher strengths which was due to the better dissolution of aluminosilicates. Moreover, since volcanic ash is relatively high in silica and alumina but deficient in calcium oxide, while GGBS is rich in calcium oxide, the coexistence of these two materials in geopolymer was more efficient, which was due to the synergic formation of N-A-S-H and C-A-S-H gels. Investigating different activator/binder ratios of 1.2, 1.4 and 1.6 demonstrated that for the samples cured in OC condition with 90 days of curing and those cured in DC condition with 28 days of curing increasing the ratio from 1.2 to 1.4 and further increase from 1.4 to 1.6, enhanced the mechanical strength, while for all of the samples the optimum ratio was 1.4. Additionally, the results of durability tests outline that geopolymer stabilized soil has a better performance against freeze-thaw cycles compared with wet-dry cycles. The samples containing 30% GGBS experienced a fewer strength reduction during durability tests in comparison with those with 0% GGBS, which sheds light on the positive effect of using GGBS to gain better performance against wet-dry and freeze-thaw cycles. Moreover, all of the microstructural analysises support the mechanical results.